Positive-working photoresist composition

ABSTRACT

Disclosed is a novel chemical-amplification positive-working photoresist composition capable of giving a patterned resist layer with excellent properties such as photosensitivy, pattern resolution, heat resistance and cross sectional profile of the patterned resist layer. The composition is characterized by the use of, as the film-forming resinous component, a hydroxyl-containing resinous ingredient which is a combination of a first resin of which from 30 to 60% of the hydroxyl groups are substituted by acid-dissociable solubility-reducing groups and a second resin of which from 5 to 20% of the hydroxyl groups are substituted by acid-dissociable groups of the same kind as in the first resin in a weight proportion of 1.9 to 9:1.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a positive-working photoresistcomposition or, more particularly, to a positive-workingchemical-amplification photoresist composition capable of being incompliance with various requirements for the performance of thephotoresist relative to photosensitivity, pattern resolution, heatresistance, focusing-depth latitude, cross sectional profile ofpatterned resist layers, holding stability of coating layers of thecomposition, dependence on the nature of the substrate surface and so onas well as good reproducibility of product quality.

[0002] As compared with conventional photoresist compositions containinga naphthoquinone diazide sulfonic acid ester as the photosensitiveingredient and a novolak resin as the film-forming ingredient,photoresist compositions of the chemical-amplification type exhibitexcellent photosensitivity and pattern resolution so that they arehighlighted in recent years in the photolithographic technology for themanufacture of fine electronic devices. As a result of extensiveinvestigations to accomplish improvements of the photoresistperformance, a great variety of chemical-amplification photoresistcompositions have been proposed, some of which are already under currentuse in the electronic industry.

[0003] Chemical-amplification photoresist compositions can be classifiedinto positive-working and negative-working photoresist compositions,each of which comprises a radiation-sensitive acid-generating agentcapable of releasing an acid by the irradiation with a radiation such asultraviolet light and a film-forming resinous ingredient which issubject to a change in the solubility behavior in an aqueous alkalinesolution by interacting with the acid.

[0004] In a positive-working photoresist composition of thechemical-amplification type, a typical film-forming resinous ingredientis a polyhydroxystyrene resin of which a part of the hydroxyl groups aresubstituted by tertiary alkoxycarbonyl groups such astert-butoxycarbonyl groups or cyclic ether groups such astetrahydropyranyl groups. In a negative-working photoresist composition,on the other hand, the film-forming resinous ingredient is a combinationof an acid-crosslinkable compound such as a melamine resin and urearesin with a polyhydroxystyrene resin unsubstituted or substituted for apart of the hydroxyl groups as mentioned above or a novolak resin.

[0005] Various proposals and attempts have been made relative to each ofthe ingredients in the chemical-amplification photoresist compositionswith an object to improve the performance of the photoresist layer inrespect of photosensitivity, pattern resolution, heat resistance,focusing-depth latitude, cross sectional profile of patterned resistlayers, holding stability of the resist layer as formed by coating,dependence on the nature of the substrate surface and other properties.

[0006] For example, a positive-working photoresist composition, in whichthe film-forming resinous ingredient is a combination of two resinshaving different kinds of the acid-dissociable substituent groups, isdisclosed in Japanese Patent Kokai 8-15864, 8-262721, 9-160244,9-179301, 9-222732, 9-222733, 10-31309 and 10-48826 and elsewhere. Aproposal is made in Japanese Patent Kokai 9-160246, 9-211868, 9-274320and 9-311452 for the use of a ternary copolymeric resin consisting ofhydroxystyrene units having acid-dissociable groups of a first type,hydroxystyrene units having acid-dissociable groups of a second type andunsubstituted hydroxystyrene units in a positive-working composition.Japanese Patent Kokai 9-236921 proposes a positive-workingphotosensitive composition containing an alkali-soluble resin havingphenolic hydroxyl groups and a weight-average molecular weight of 6000to 60000 including 10% by weight or less of the fraction of a molecularweight smaller than 4000 and at least 80% by weight of the fraction of amolecular weight of 4000 to 70000. Japanese Patent Kokai 9-90639proposes a positive-working composition in which the resinous ingredientis a combination of a high molecular weight polymer substituted byacid-dissociable groups having a molecular weight dispersion of 1.5 orsmaller and a low molecular weight polymer substituted byacid-dissociable groups having a molecular weight dispersion of 5.0 orsmaller with the proviso that the ratio of the high and lowweight-average molecular weights of the resins is at least 1.5. JapanesePatent Kokai 7-199468 proposes a photosensitive composition containing acompound of low polarity of the molecules to exhibit a low dissolvingvelocity in alkali and another compound of high polarity of themolecules to exhibit a high dissolving velocity in alkali.

[0007] As these chemical-amplification positive-working photoresistcompositions are produced and consumed in large quantities, variousproblems have to be solved by the producers thereof in connection withthe matter of quality control in order to fully comply with the needs ofthe consumers.

[0008] As for the base resin as the film-forming resinous ingredientplaying an important role in the photoresist composition, for example, aserious problem is in the low reproducibility in the quality of theresin products among the preparation lots even if the preparationconditions are controlled constant sometimes leading to an unacceptableproduct quality. Another problem recently under attention is occurrenceof surface defects in the patterned resist layer after development alongwith the introduction of the surface-defect tester called KLA (a tradename) into the production line of the photoresist consumers.

[0009] Along with the recent trend in the semiconductor industriestoward finer and finer patterning, some of the photoresist consumersrequest very delicate modification of the photoresist properties tocomply with variations in the exposure light system, nature of thesubstrate surface, condition of pattern isolation and so on so that theresinous ingredients in the compositions also must comply with therespective requests of the consumers.

SUMMARY OF THE INVENTION

[0010] Under the above described technological situations, the presentinvention has an object to provide a chemical-amplificationpositive-working photoresist composition having good adaptability to thequality variation among the production lots of the base resin for theresinous film-forming ingredient thus to provide various grades ofphotoresist products to comply with so diversified requirements of thephotoresist consumers.

[0011] Thus, the chemical-amplification positive-working photoresistcomposition of the present invention is a uniform solution in an organicsolvent, which comprises:

[0012] (A) a polyhydroxystyrene-based resinous ingredient of which thehydroxyl groups are partly substituted by acid-dissociable substituentgroups capable of being dissociated by interacting with an acid; and

[0013] (B) a radiation-sensitive acid-generating compound capable ofreleasing an acid by irradiation with a radiation, the resinousingredient (A) being a combination comprising (A1) a first substitutedpolyhydroxystyrene resin and (A2) a second substitutedpolyhydroxystyrene resin, the substituent groups in the first and secondresins (A1) and (A2) being of the same kind, of which the degree ofsubstitution by the substituent groups for a part of the hydroxyl groupsin the first resin (A1) is larger than that in the second resin (A2)with the proviso that the ratio of the maximum weight-average molecularweight Mw_(max) to the minimum weight-average molecular weight Mw_(min)in each of the first and second resins (A1) and (A2), i.e.Mw_(max):Mw_(min), does not exceed 1.5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] It is essential that, in the inventive photoresist composition,the resinous ingredient (A) is a combination of two polyhydroxystyreneresins substituted by acid-dissociable groups for a part of the hydroxylgroups in different degrees of substitution each from the other. Theacid-dissociable substituent group must have an effect of insolubilizingthe polyhydroxystyrene resin substituted thereby in an aqueous alkalinesolution while the substituent groups are dissociated by interactingwith an acid when irradiated with a radiation so as to increase thesolubility of the resin in an aqueous alkaline solution.

[0015] The substituted hydroxyl group-containing resinous compoundusable in the inventive photoresist composition is not particularlylimitative and can be selected from those used in conventionalchemical-amplification positive-working photoresist compositions withoutparticular limitations. In order to accomplish adequate alkalisolubility, adhesive bondability to the substrate surface and heatresistance, a preferable resinous compound is a polyhydroxystyrene resinof which a part of the hydroxyl groups are substituted by theacid-dissociable alkali solubility-reducing substituent groups.

[0016] Any types of known acid-dissociable substituent groups can beused in the resinous ingredient (A) in the present invention byselecting from those conventionally utilized in chemical-amplificationpositive-working photoresist compositions. Tertiary alkoxycarbonylgroups, tertiary alkyl groups, alkoxyalkyl groups and cyclic ethergroups are preferred in consideration of their good acid-dissociability,heat resistance and cross sectional profile of the patterned resistlayer.

[0017] The tertiary alkoxycarbonyl group is exemplified bytert-butyloxycarbonyl and tert-amyloxycarbonyl groups. The tertiaryalkyl group is exemplified by tert-butyl and tert-amyl groups. Thealkoxyalkyl group is exemplified by 1-ethoxyethyl and 1-methoxypropylgroups. The cyclic ether group is exemplified by tetrahydropyranyl andtetrahydrofuranyl groups.

[0018] Polymeric resins having hydroxystyrene units substituted for thehydroxyl group by the above named acid-dissociable substituent groupinclude (1) a polyhydroxystyrene resin of which from 5 to 60% of thehydroxyl groups are substituted by the acid-dissociable substituentgroups selected from those mentioned above and (2) a polyhydroxystyreneresin of which from 10 to 49% of the hydroxyl groups are substituted bythe acid-dissociable substituent groups selected from tertiaryalkoxycarbonyl groups, tertiary alkyl groups and cyclic ether groups andfrom 10 to 49% of the hydroxyl groups are substituted by alkoxyalkylgroups.

[0019] Examples of the combinations of polymeric compounds suitable asthe component (A) in the inventive photoresist composition include (a1)a combination of a first polyhydroxystyrene resin of which from 30 to60% of the hydroxyl groups are substituted by tert-butoxycarbonyl groupsand a second polyhydroxystyrene resin of which from 5 to 20% of thehydroxyl groups are substituted by tert-butoxycarbonyl groups, (a2) acombination of a first polyhydroxystyrene resin of which from 30 to 60%of the hydroxyl groups are substituted by tetrahydropyranyl groups and asecond polyhydroxystyrene resin of which from 5 to 20% of the hydroxylgroups are substituted by tetrahydropyranyl groups and (a3) acombination of a first polyhydroxystyrene resin of which from 30 to 60%of the hydroxyl groups are substituted by 1-ethoxyethyl groups and asecond polyhydroxystyrene resin of which from 5 to 20% of the hydroxylgroups are substituted by 1-ethoxyethyl groups.

[0020] Other examples of suitable combinations include (a4) acombination of two copolymers each consisting of from 10 to 49% by molesof the hydroxystyrene units substituted by tert-butoxycarbonyl groups,from 10 to 49% by moles of the hydroxystyrene units substituted by1-ethoxyethyl groups and from 2 to 80% by moles of unsubstitutedhydroxystyrene units assuming that the total degrees of substitution forthe hydroxyl groups are different between the two resins, (a5) acombination of two copolymers each consisting of from 10 to 49% by molesof the hydroxystyrene units substituted by tert-butyl groups, from 10 to49% by moles of the hydroxystyrene units substituted by 1-ethoxyethylgroups and from 2 to 80% by moles of unsubstituted hydroxystyrene unitsassuming that the total degrees of substitution for the hydroxyl groupsare different between the two resins and (a6) a combination of twocopolymers each consisting of from 10 to 49% by moles of thehydroxystyrene units substituted by tetrahydropyranyl groups, from 10 to49% by moles of the hydroxystyrene units substituted by 1-ethoxyethylgroups and from 2 to 80% by moles of unsubstituted hydroxystyrene unitsassuming that the total degrees of substitution for the hydroxyl groupsare different between the two resins.

[0021] Each of the above described polymeric resins should have aweight-average molecular weight in the range from 2000 to 50000 or,preferably, from 5000 to 15000 and the molecular weight dispersion givenby the ratio of the weight-average molecular weight Mw to thenumber-average molecular weight Mn, i.e. Mw:Mn, does not exceed 5.0 or,preferably, does not exceed 2.0 since the molecular weight dispersionshould be as small as possible in order to accomplish improvements inthe pattern resolution and heat resistance of the resist.

[0022] The resinous ingredient (A) in the inventive composition is acombination of at least two kinds of the above describedpolyhydroxystyrene-based resins while, in each of the constituentresins, the ratio of the maximum weight-average molecular weightMw_(max) to the minimum weight-average molecular weight Mw_(min), i.e.Mw_(max):Mw_(min), should be smaller than 1.5 or, preferably, smallerthan 1.3 or, more preferably, about 1.0. This limitation serves toensure uniformity of the respective polymeric resins.

[0023] It is essential that the acid-dissociable substituent groups inone of the respective polymeric resins constituting the combination areof the same kind as those in the other constituent resins havingdifferent degrees of substitution. This limitation has an effect toensure different velocities of dissolving in an aqueous alkalinesolution so that the photoresist layer of the inventive composition canbe developed with good uniformity in the light-exposed areas to suppressoccurrence of surface defects.

[0024] Assuming that the resinous ingredient (A) in the inventivecomposition is a combination of first and secondpolyhydroxystyrene-based polymeric resins (A1) and (A2), in particular,the degrees of substitution for a part of the hydroxyl groups in thefirst and second resins are preferably in the ranges of from 30 to 60%and from 5 to 20%, respectively, or, preferably, from 35 to 60% and from5 to 15%, respectively, since the difference in the degrees ofsubstitution between the two polymeric resins should preferably be aslarge as possible in order to fully suppress occurrence of surfacedefects in the photoresist layer.

[0025] When the polyhydroxystyrene-based resins constituting theresinous ingredient (A) satisfy all of the above described requirements,occurrence of surface defects after development of the resist layer canbe fully prevented without adversely affecting other properties such asphotosensitivity, pattern resolution and cross sectional profile of thepatterned resist layer.

[0026] The compounding proportion of the two kinds or more of thepolyhydroxystyrene-based resins forming the combination as the resinousingredient (A) of the inventive composition can be readily selected bymaking reference to the dissolving velocity of the resinous ingredientin an aqueous alkaline solution. For example, an appropriate substrateis provided with a coating layer of the component (A) and immersed in a2.38% by weight aqueous solution of tetramethylammonium hydroxide todetermine the rate of thickness reduction of the coating layer. Namely,the compounding proportion of the constituent resins is selected suchthat the above mentioned rate of thickness reduction does not exceed 100nm per minute at 23° C.

[0027] When the component (A) is the above described combination (a1),for example, the mixing proportion of the two resins is selected suchthat the above mentioned velocity does not exceed 100 nm/minute at 23°C. by considering that the velocities of the first and second resins are0 to 50 nm/minute and 100 to 300 nm/minute, respectively.

[0028] Similarly, the mixing proportion of the two resins in thecombination (a2) is selected such that the above mentioned velocity doesnot exceed 100 nm/minute at 23° C. by considering that the velocities ofthe first and second resins are 0 to 50 nm/minute and 100 to 300nm/minute, respectively. Further, the mixing proportion of the tworesins in the combination (a3) is selected such that the above mentionedvelocity does not exceed 100 nm/minute at 23° C. by considering that thevelocities of the first and second resins are 0 to 50 nm/minute and 100to 300 nm/minute, respectively.

[0029] It is usual in order to effectively prevent occurrence of surfacedefects in the patterned resist layer after development that the firstpolymeric resin and the second polymeric resin are combined in a weightproportion in the range from 1:9 to 9:1 or, preferably, from 4:6 to 1:9.In order to accomplish further improvement in the resist characteristicssuch as photosensitivity, pattern resolution and cross sectional profileof the patterned resist layer, it is preferable that the component (A)is a mixture of the combinations (a1) and (a3) or a mixture of thecombinations (a2) and (a3).

[0030] In the positive-working photoresist composition of the invention,the acid-generating agent as the component (B), which releases an acidby the irradiation with a radiation, is not particularly limitative andcan be selected from those known compounds used as an acid-generatingagent in the prior art photoresist compositions of thechemical-amplification type without particular limitations. Examples ofsuitable acid-generating compounds include diazomethane compounds,nitrobenzyl derivatives, sulfonic acid esters, onium salts, benzointosylate compounds, halogen-containing triazine compounds and cyanogroup-containing oxime sulfonate compounds, of which diazomethanecompounds and onium salts of which the anionic part is formed from ahalogenoalkyl sulfonic acid having 1 to 15 carbon atoms are preferable.

[0031] The diazomethane compound is exemplified bybis(p-toluenesulfonyl) diazomethane, bis(1,1-dimethylethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl) diazomethane andbis(2,4-dimethylphenylsulfonyl) diazomethane. The onium salt abovementioned is exemplified by bis(4-methoxyphenyl)iodoniumtrifluoromethane sulfonate, bis(p-tert-butylphenyl)iodoniumtrifluoromethane sulfonate, (4-methoxyphenyl)diphenylsulfoniumtrifluoromethane sulfonate and (p-tert-butylphenyl)diphenyl sulfoniumtrifluoromethane sulfonate.

[0032] The above named various acid-generating compounds can be used asthe component (B) either singly or as a combination of two kinds or moreaccording to need. The amount of the component (B) is in the range,usually, from 0.5 to 30 parts by weight or, preferably, from 1 to 10parts by weight per 100 parts by weight of the resinous ingredient asthe component (A). When the amount of the component (B) is too small,images for patterning cannot be formed while, when the amount thereof istoo large, difficulties are encountered in the preparation of thecomposition in the form of a uniform solution suitable for coating or,even if the composition could be prepared, the solution suffers adecrease in the storage stability.

[0033] The positive-working photoresist composition of the presentinvention is prepared by uniformly dissolving the components (A) and (B)each in a specified amount in a suitable organic solvent. Though notparticularly limitative, examples of preferable organic solventsinclude, in respect of the coating workability of the photoresistcomposition and prevention of occurrence of surface defects,propyleneglycol monoalkyl ether acetates such as propyleneglycolmonomethyl ether acetate as well as mixtures thereof with lower alkyllactates such as methyl lactate, ethyl lactate, butyl lactate and pentyllactate or propyleneglycol mono(lower alkyl) ethers such aspropyleneglycol monomethyl ether and propyleneglycol monoethyl ether.

[0034] It is optional that the positive-working photoresist compositionof the invention is compounded according to need, in addition to theabove described components (A) and (B), with various kinds of knownadditives including amine compounds to improve the holding stability ofthe resist coating layer or to prevent excessive diffusion of the acidgenerated from the component (B), carboxylic acids to improve thephotosensitivity of the composition and halation-preventing agents eachin a limited amount.

[0035] The procedure for the photolithographic patterning work by usingthe positive-working photoresist composition of the invention can beconventional. Namely, a substrate such as a semiconductor silicon waferis coated with the photoresist composition in the form of a uniformsolution on a suitable coating machine such as a spinner followed bydrying to form a resist layer which is pattern-wise exposed to aradiation such as ultraviolet light, deep ultraviolet light, excimerlaser beams and the like on a minifying projection light-exposuremachine through a photomask bearing a desired pattern or irradiated byscanning of electron beams according to the desired pattern to form alatent image of the pattern followed by a post-exposure bakingtreatment. Thereafter, the latent image is developed in a developmenttreatment by using an aqueous alkaline solution such as a 1 to 10% byweight aqueous solution of tetramethylammonium hydroxide to dissolveaway the resist layer in the exposed areas leaving a patterned resistlayer having fidelity to the photomask pattern.

[0036] In the following, the present invention is described in moredetail by way of Examples, which, however, never limit the scope of theinvention in any way, as preceded by a description of the testingprocedures for the evaluation of the photoresist compositions andReference Examples for preparation and characterization of thecombination of two different resins as the component (A). In thefollowing description, the term of “parts” always refers to “parts byweight”.

[0037] (1) Photosensitivity of the Photoresist Composition

[0038] A silicon wafer was coated with the photoresist composition on aspinner followed by drying on a hot plate at 90° C. for 90 seconds toform a dried resist layer having a thickness of 0.7 μm. The resist layerwas exposed to light on a minifying projection exposure machine (ModelNSR-2005EX8A, manufactured by Nikon Co.) in step-wise increased exposuredose by an increment of 1 mJ/cm² followed by a post-exposure bakingtreatment at 110° C. for 90 seconds and then subjected to a developmenttreatment at 23° C. for 60 seconds in a 2.38% by weight aqueous solutionof tetramethylammonium hydroxide followed by rinse with water for 30seconds and drying. The minimum exposure dose by which the resist layeron the substrate surface had been completely dissolved away was taken asthe photosensitivity of the composition.

[0039] (2) Cross Sectional Profile of Patterned Resist Layer

[0040] A line-and-space patterned resist layer of 0.25 μm line widthformed in the same manner as in (1) above was examined on a scanningelectron microscopic photograph for the cross section and the resultswere rated as A for a good orthogonal profile, B for an upwardlynarrowing profile and C for a profile with a rounded top flat andtrailing skirts.

[0041] (3) Pattern Resolution

[0042] Resist layers were patterned in line-and-space patterns of variedline widths in the same manner as in (1) above and the critical linewidth was recorded as the pattern resolution.

[0043] (4) Surface Defects

[0044] A resist layer patterned in the same manner as in (1) above on a8 inch silicon wafer was examined by using a surface-defects tester(Model KLA, manufactured by KLA Co.) and the number of defects wascounted on the silicon wafer and recorded.

[0045] (5) Heat Resistance

[0046] A line-and-space patterned resist layer of 0.25 μm line widthformed in the same manner as in (1) above was heated on a hot plate at120° C. for 90 seconds. Thereafter, the cross sectional profile of thepatterned resist layer was examined on a scanning electron microscopicphotograph to record the results as A for an orthogonal profile and Bfor a profile showing thermal flow of the resist layer.

REFERENCE EXAMPLE 1

[0047] A solution of a base resin for the photoresist composition wasprepared by dissolving, in 400 parts of propyleneglycol monomethyl etheracetate, 40 parts of a first partially substituted polyhydroxystyreneresin, of which 45% of the hydroxyl groups were substituted bytert-butoxycarbonyl groups, having a weight-average molecular weight of10000 with a molecular weight dispersion of 1.2 and exhibiting nodissolution in a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide and 60 parts of a second partially substitutedpolyhydroxystyrene resin, of which 20% of the hydroxyl groups weresubstituted by tert-butoxycarbonyl groups, having a weight-averagemolecular weight of 10000 with a molecular weight dispersion of 1.2 andexhibiting a dissolving velocity of 150 nm/minute in a 2.38% by weightaqueous solution of tetramethylammonium hydroxide.

[0048] A coating layer formed on a silicon wafer by coating with theabove prepared solution of the base resin combination followed by dryingexhibited a dissolving velocity of 30 nm/minute under the same testingconditions.

REFERENCE EXAMPLE 2

[0049] A solution of a base resin for the photoresist composition wasprepared by dissolving, in 400 parts of propyleneglycol monomethyl etheracetate, 30 parts of a first partially substituted polyhydroxystyreneresin, of which 50% of the hydroxyl groups were substituted bytetrahydropyranyl groups, having a weight-average molecular weight of10000 with a molecular weight dispersion of 1.2 and exhibiting nodissolution in a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide and 70 parts of a second partially substitutedpolyhydroxystyrene resin, of which 15% of the hydroxyl groups weresubstituted by tetrahydropyranyl groups, having a weight-averagemolecular weight of 10000 with a molecular weight dispersion of 1.2 andexhibiting a dissolving velocity of 170 nm/minute in a 2.38% by weightaqueous solution of tetramethylammonium hydroxide.

[0050] A coating layer formed on a silicon wafer by coating with theabove prepared solution of the base resin combination followed by dryingexhibited a dissolving velocity of 20 nm/minute under the same testingconditions.

REFERENCE EXAMPLE 3

[0051] A solution of a base resin for the photoresist composition wasprepared by dissolving, in 400 parts of propyleneglycol monomethyl etheracetate, 45 parts of a first partially substituted polyhydroxystyreneresin, of which 45% of the hydroxyl groups were substituted by1-ethoxyethyl groups, having a weight-average molecular weight of 10000with a molecular weight dispersion of 1.2 and exhibiting a dissolvingvelocity of 5 nm/minute in a 2.38% by weight aqueous solution oftetramethylammonium hydroxide and 55 parts of a second partiallysubstituted polyhydroxystyrene resin, of which 25% of the hydroxylgroups were substituted by 1-ethoxyethyl groups, having a weight-averagemolecular weight of 10000 with a molecular weight dispersion of 1.2 andexhibiting a dissolving velocity of 130 nm/minute in a 2.38% by weightaqueous solution of tetramethylammonium hydroxide.

[0052] A coating layer formed on a silicon wafer by coating with theabove prepared solution of the base resin combination followed by dryingexhibited a dissolving velocity of 40 nm/minute under the same testingconditions.

REFERENCE EXAMPLE 4

[0053] A solution of a base resin for the photoresist composition wasprepared by dissolving, in 400 parts of propyleneglycol monomethyl etheracetate, 45 parts of the same first partiallytert-butoxycarbonyl-substituted polyhydroxystyrene resin as used inReference Example 1 and 55 parts of a second partially substitutedpolyhydroxystyrene resin, of which 20% of the hydroxyl groups weresubstituted by tert-butoxycarbonyl groups, having a weight-averagemolecular weight of 5000 with a molecular weight dispersion of 1.2 andexhibiting a dissolving velocity of 160 nm/minute in a 2.38% by weightaqueous solution of tetramethylammonium hydroxide.

[0054] A coating layer formed on a silicon wafer by coating with theabove prepared solution of the base resin combination followed by dryingexhibited a dissolving velocity of 30 nm/minute under the same testingconditions.

REFERENCE EXAMPLE 5

[0055] A solution of a base resin for the photoresist composition wasprepared by dissolving, in 400 parts of propyleneglycol monomethyl etheracetate, 35 parts of the same first partiallytetrahydropyranyl-substituted polyhydroxystyrene resin as used inReference Example 2 and 65 parts of a second partially substitutedpolyhydroxystyrene resin, of which 15% of the hydroxyl groups weresubstituted by tetrahydropyranyl groups, having a weight-averagemolecular weight of 5000 with a molecular weight dispersion of 1.2 andexhibiting a dissolving velocity of 180 nm/minute in a 2.38% by weightaqueous solution of tetramethylammonium hydroxide.

[0056] A coating layer formed on a silicon wafer by coating with theabove prepared solution of the base resin combination followed by dryingexhibited a dissolving velocity of 20 nm/minute under the same testingconditions.

REFERENCE EXAMPLE 6

[0057] A solution of a base resin for the photoresist composition wasprepared by dissolving, in 400 parts of propyleneglycol monomethyl etheracetate, 50 parts of the same first partially 1-ethoxyethyl-substitutedpolyhydroxystyrene resin as used in Reference Example 3 and 50 parts ofa second partially substituted polyhydroxystyrene resin, of which 25% ofthe hydroxyl groups were substituted by 1-ethoxyethyl groups, having aweight-average molecular weight of 5000 with a molecular weightdispersion of 1.2 and exhibiting a dissolving velocity of 150 nm/minutein a 2.38% by weight aqueous solution of tetramethylammonium hydroxide.

[0058] A coating layer formed on a silicon wafer by coating with theabove prepared solution of the base resin combination followed by dryingexhibited a dissolving velocity of 40 nm/minute under the same testingconditions. Example 1.

[0059] A positive-working photoresist composition was prepared bydissolving, in 490 parts of propyleneglycol monomethyl ether acetate, 30parts of the same combination of the two partiallytert-butoxycarbonyl-substituted resins as in Reference Example 1, 70parts of the same combination of the two partially1-ethoxyethyl-substituted resins as in Reference Example 3, 7 parts ofbis(cyclohexylsulfonyl) diazomethane, 0.1 part of triethylamine and 0.5part of salicylic acid followed by filtration of the solution through amembrane filter of 0.2 μm pore diameter.

[0060] This positive-working photoresist composition was subjected tothe evaluation tests of the above described testing items (1) to (5) toobtain results including:

[0061] (1) 15 mJ/cm² of the photosensitivity;

[0062] (2) grade A of the cross sectional profile of the patternedresist layer;

[0063] (3) 0.20 μm of the pattern resolution;

[0064] (4) 5 per wafer of the surface defects; and

[0065] (5) grade A of the heat resistance.

EXAMPLE 2

[0066] The formulation of the positive-working photoresist compositionand the evaluation procedure thereof were substantially the same as inExample 1 excepting for the replacement of the combination of thepartially tert-butoxycarbonyl-substituted polyhydroxystyrene resins withthe same amount of the resin combination corresponding to ReferenceExample 2.

[0067] The results of the evaluation tests of this photoresistcomposition for the testing items (1) to (5) were as follows including:

[0068] (1) 16 mJ/cm² of the photosensitivity;

[0069] (2) grade A of the cross sectional profile of the patternedresist layer;

[0070] (3) 0.20 μm of the pattern resolution;

[0071] (4) 7 per wafer of the surface defects; and

[0072] (5) grade A of the heat resistance.

COMPARATIVE EXAMPLE 1

[0073] A positive-working photoresist composition was prepared bydissolving, in 490 parts of propyleneglycol monomethyl ether acetate, 30parts of the same combination of the two partiallytert-butoxycarbonyl-substituted resins as in Reference Example 4, 70parts of the same combination of the two partially1-ethoxyethyl-substituted resins as in Reference Example 6, 7 parts ofbis(cyclohexylsulfonyl) diazomethane, 0.1 part of triethylamine and 0.5part of salicylic acid followed by filtration of the solution through amembrane filter of 0.2 μm pore diameter.

[0074] The results of the evaluation tests of this comparativephotoresist composition for the testing items (1) to (5) were as followsincluding:

[0075] (1) 15 mJ/cm² of the photosensitivity;

[0076] (2) grade A of the cross sectional profile of the patternedresist layer;

[0077] (3) 0.20 μm of the pattern resolution;

[0078] (4) 1000 per wafer of the surface defects; and

[0079] (5) grade B of the heat resistance.

COMPARATIVE EXAMPLE 2

[0080] The formulation of the positive-working photoresist compositionand the evaluation procedure thereof were substantially the same as inComparative Example 1 excepting for the replacement of the combinationof the partially tert-butoxycarbonyl-substituted polyhydroxystyreneresins with the same amount of the resin combination corresponding toReference Example 5.

[0081] The results of the evaluation tests of this comparativephotoresist composition for the testing items (1) to (5) were as followsincluding:

[0082] (1) 16 mJ/cm² of the photosensitivity;

[0083] (2) grade A of the cross sectional profile of the patternedresist layer;

[0084] (3) 0.20 μm of the pattern resolution;

[0085] (4) 1500 per wafer of the surface defects; and

[0086] (5) grade B of the heat resistance.

What is claimed is:
 1. A chemical-amplification positive-workingphotoresist composition which comprises, as a uniform solution in anorganic solvent: (A) a polyhydroxystyrene-based resinous ingredient ofwhich the hydroxyl groups are partly substituted by acid-dissociablesubstituent groups capable of being dissociated by interacting with anacid; and (B) a radiation-sensitive acid-generating compound capable ofreleasing an acid by irradiation with a radiation, the resinousingredient as the component (A) being a combination comprising (A1) afirst polyhydroxystyrene resin substituted for a part of the hydroxylgroups by acid-dissociable substituent groups and (A2) a secondpolyhydroxy-styrene resin substituted for a part of the hydroxyl groupsby acid-dissociable substituent groups which are the same as in thefirst polyhydroxystyrene resin (A1), of which the degree of substitutionby the substituent groups for a part of the hydroxyl groups in the firstpolyhydroxystyrene resin (A1) is larger than the degree of substitutionin the second polyhydroxystyrene resin (A2) with the proviso that theratio of the maximum weight-average molecular weight Mw_(max) to theminimum weight-average molecular weight Mw_(min) in the first and secondpolyhydroxystyrene resins (A1) and (A2) is smaller than 1.5.
 2. Thechemical-amplification positive-working photoresist composition asclaimed in claim 1 in which the overall degree of substitution in theresinous ingredient as the component (A) for a part of the hydroxylgroups by the acid-dissociable substituent groups is in the range from 5to 60%.
 3. The chemical-amplification positive-working photoresistcomposition as claimed in claim 1 in which the acid-dissociablesubstituent group is selected from the group consisting of tertiaryalkoxycarbonyl groups, tertiary alkyl groups, alkoxyalkyl groups andcyclic ether groups.
 4. The chemical-amplification positive-workingphotoresist composition as claimed in claim 3 in which theacid-dissociable substituent group is selected from the group consistingof tert-butoxycarbonyl group, tert-butyl group, tetrahydropyranyl group,tetrahydrofuranyl group, 1-ethoxyethyl group and 1-methoxypropyl group.5. The chemical-amplification positive-working photoresist compositionas claimed in claim 1 in which the polyhydroxystyrene-based resinousingredient as the component (A) is a combination of (A1) a firstpolyhydroxystyrene resin substituted for from 30 to 60% of the hydroxylgroups by the acid-dissociable substituent groups and (A2) a secondpolyhydroxystyrene resin substituted for from 5 to 20% of the hydroxylgroups by the acid-dissociable substituent groups.
 6. Thechemical-amplification positive-working photoresist composition asclaimed in claim 5 in which the polyhydroxystyrene-based resinousingredient as the component (A) is a combination of the first and secondpolyhydroxystyrene resins (A1) and (A2) in a weight proportion in therange from 1:9 to 9:1.
 7. The chemical-amplification positive-workingphotoresist composition as claimed in claim 5 in which thepolyhydroxystyrene-based resinous ingredient as the component (A) is acombination of (A1) a first polyhydroxystyrene resin substituted forfrom 35 to 60% of the hydroxyl groups by the acid-dissociablesubstituent groups and (A2) a second polyhydroxystyrene resinsubstituted for from 5 to 15% of the hydroxyl groups by theacid-dissociable substituent groups.
 8. The chemical-amplificationpositive-working photoresist composition as claimed in claim 7 in whichthe polyhydroxystyrene-based resinous ingredient as the component (A) isa combination of the first and second polyhydroxystyrene resins (A1) and(A2) in a weight proportion in the range from 4:6 to 1:9.
 9. Thechemical-amplification positive-working photoresist composition asclaimed in claim 5 in which the polyhydroxystyrene-based resinousingredient as the component (A) is a combination of (A1) a firstpolyhydroxystyrene resin substituted for from 30 to 60% of the hydroxylgroups by tert-butoxycarbonyl groups and (A2) a secondpolyhydroxystyrene resin substituted for from 5 to 20% of the hydroxylgroups by tert-butoxycarbonyl groups.
 10. The chemical-amplificationpositive-working photoresist composition as claimed in claim 1 in whichthe ratio of the maximum weight-average molecular weight Mw_(max) to theminimum weight-average molecular weight Mw_(min) in the first and secondpolyhydroxystyrene resins (A1) and (A2) is smaller than 1.3.